Overview of Recent Three-Dimensional, Small-Scale, Mini-Pipe Testing of Carbon Steel Well Tubulars with Internal Pressure, Axial Load, and Internal/External Hydrogen Sulfide Exposure Available to Purchase

Mini-pipe testing has been used to expose miniature low-alloy carbon steel pipes to one-sided and two-sided hydrogen sulfide (H₂S) combined with high internal pressures (20,000+ psi) and axial loads. This paper explains the types of tests that have been performed and the results that have been observed. One-sided vs two-sided H₂S exposure combined with stress gradients across the pipe wall is shown to lead to differences in pipe performance. Test results indicate a substantial increase in pipe material performance when one-sided H₂S exposure is taken into account compared with two-sided H₂S exposure. Tests of prenotched mini-pipes are introduced, which indicate that a fracture mechanics formula using K_ISSC from the double-cantilever beam (DCB) test is nonconservative and overpredicts the pipe failure pressure due to sulfide stress cracking. Use of the limiting value, K_ISSC-Limit, is shown to improve the prediction of pipe cracking failure significantly, making it almost conservative. Use of K_ISSC-Limit combined with a design factor accounting for DCB uncertainty finally makes the fracture formula a conservative predictor of C110 pipe cracking. Tests of mini-pipes without preexisting notches are shown to indicate that a fracture mechanics formula alone cannot reliably predict pipe cracking performance; i.e., the tests indicate that both a three-dimensional stress formula and an improved fracture mechanics formula are needed to conservatively predict pipe material performance in H₂S. The tests of mini-pipes have been consistent with tests conducted by the American Petroleum Institute (API, Washington, DC) on full-sized casing. Three-dimensional mini-pipe testing is shown to be a tool to better understand and quantify pipe per formance in H₂S. Results to date suggest that much understanding and benefit can be gained through additional three-dimensional testing by the sour testing community.